1. Field of the Invention
The invention relates generally to arc lamps and specifically to devices and methods used to cool the anode electrode of arc lamps.
2. Description of the Prior Art
Short arc lamps provide intense point sources of light that allow light collection in reflectors for applications in medical endoscopes, instrumentation and projection. Also, short arc lamps are used in industrial endoscopes, for example in the inspection of jet engine interiors.
A typical short arc lamp comprises an anode and a cathode positioned along the longitudinal axis of a cylindrical, sealed concave chamber that contains a gas pressurized to several atmospheres. U.S. Pat. 4,633,128, issued Dec. 30, 1986, to Roy D. Roberts, the present inventor, and Robert L. Miner, describes such a short arc lamp in which a copper sleeve member is attached to the reflecting wall to conduct heat from the reflecting wall through to the exterior wall and eventually to circulating ambient air.
The lamp illustrated in Roberts. et al., can be operated at one kilowatt. At higher power levels, the heat generated by an electric arc between the cathode and anode electrodes encounters thermal resistance to the surrounding areas which may result in overheating and potential failure. When too much power is applied to such lamps, thermal gradients within the ceramic lamp body may cause cracks and possibly a dangerous explosion of the lamp.
Conventional short arc lamps have solid anodes that tend to get very hot at the center of the face supporting the arc. If a portion of the electrode metal gets too hot, it vaporizes, and black deposits will form on the reflector. Such deposits reduce the reflector's ability to tend off heat absorption, and a catastrophic thermal runaway can develop.
At power levels of three thousand watts, heat management becomes the most limiting factor. A fine balance must always be struck between long lamp life and useful lamp output and efficiency.